Speakerphones allow telephones, including mobile telephones and corded or cordless conventional telephones, to be used hands-free. Speakerphones generally utilize a speaker to project sounds, including dial tones or sounds received from the other end of a telephone call. Speakerphones also utilize a microphone to detect a user's voice or other sounds near the speakerphone so that these sounds may be transmitted.
Since the speaker of a speakerphone is typically located in close proximity to the microphone, it is possible for feedback (e.g., echo, oscillation, etc.) to occur if the microphone picks up and transmits sounds coming from the speaker. Accordingly, speakerphones typically implement either full-duplex or half-duplex functions to prevent feedback. A speakerphone with full-duplex functionality permits a user to simultaneously speak and hear what a caller is saying. To prevent feedback, such full-duplex systems typically filter out the speaker signal from the microphone pickup. In contrast, a half-duplex speakerphone typically prevents feedback by enabling one of the speaker or the microphone at any given time. Other two-way communication devices besides speakerphones, such as walkie-talkies and other radio communication devices, also often implement half-duplex functionality.
Implementing half-duplex functionality into a speakerphone generally includes a half-duplexer component that determines whether to send or receive sounds. Typically, this component is capable of determining whether a dial tone is present on the phone line, whether a caller at the other end of a call is speaking or making other sounds, and whether the user of the speakerphone is speaking or making other sounds into the microphone. Furthermore, this half-duplexer should typically be capable of controlling the signals that are transmitted to the speaker and/or the other end of a telephone call based on these determinations.